1. Technical Field
The present invention relates to an electrophotographic photoreceptor used in an image forming apparatus, such as a photocopier that forms an image using an electrophotography method, to a process cartridge, and to an image forming apparatus.
2. Related Art
Recently, an electrophotography method has been extensively applied to an image forming apparatus, such as a photocopier or a printer. Since an electrophotographic photoreceptor (hereinafter, occasionally referred to as ‘photoreceptor’) that is used in the image forming apparatus using the electrophotography method is exposed to various types of contacts or stresses in the device, deterioration may occur. Meanwhile, high reliability is required in accordance with digitalization or colorization of the image forming apparatus.
Of the photoreceptors, currently, an organic photoreceptor is extensively used. The organic photoreceptor is inexpensive in comparison with the photoreceptor including amorphous silicon, and is better in view of safety in comparison with the photoreceptor including selenium or cadmium sulfide. However, since the organic photoreceptor has low hardness as compared to the photoreceptor including selenium or cadmium sulfide, if the organic photoreceptor is repeatedly used in the image forming apparatus, undesirably, abrasion may occur due to friction to a cleaning member or a developer. If the photoreceptor is abraded, there are problems in that a life is reduced and replacement is needed in a short cycle. Additionally, since surface roughness is increased due to the friction, slidability may deteriorate.
To avoid the above-mentioned problems, a hard film that is formed of diamond-like carbon (DLC), amorphous carbon nitride (CN), or amorphous silicon nitride may be formed on the organic photoreceptor as a surface protective layer.
However, if the surface protective layer having hardness significantly different from that of the organic photoreceptor is directly formed on the organic photoreceptor, problems, such as crevices, cracks, or stripping, may occur due to a difference in hardness.
Furthermore, in the photoreceptor having excellent surface wear resistance, such as the photoreceptor using amorphous silicon or the organic photoreceptor having the surface protective layer, such as DLC, in the case of when the photoreceptor is repeatedly used in a high humidity atmosphere, the surface of the photoreceptor has low resistance due to the substance stuck to the surface of the photoreceptor. Thus, blurring occurs or reduction in concentration occurs on an image.
The reason for this is believed that the discharge product stuck to the surface of the photoreceptor is reacted with water in air to reduce electric resistance of the surface. The typical organic photoreceptor does not suffer from the above-mentioned problem because the photoreceptor itself is worn to remove the stuck substance, such as the discharge product. However, when the hard surface layer is formed on the organic photoreceptor, the above-mentioned problem may occur.
In connection with this, it is known that if the surface of the polymer material is exposed to plasma, a crosslinking structure is formed on the surface of the polymer material, thus reforming the surface of the polymer material which is exposed to the plasma. In detail, treatment using plasma of various types of gases, such as inert gas including He or Ne, nitrogen, oxygen, or hydrogen has been performed. The effect obtained through the treatment depends on the plasma treatment condition, such as the type of gas. Examples of the effect include improvement in surface property, such as adhesion strength and hydrophilicity. Additionally, it is known that the crosslinking structure is formed by the plasma treatment to improve the surface hardness of the polymer material.
For example, it is known that if the surface of the polymer material is treated using plasma of organic silicon gas, Vickers hardness is improved with 10 to 30 times, surface resistance is reduced, and an erasing effect is assured.
As examples of the plasma treatment of the organic electrophotographic photoreceptor, there are surface treatment using plasma of fluorine compound gas to obtain water repellency and film formation surface treatment that is performed when a surface coating layer is formed to improve adhesion strength of the film. However, improvement in wear resistance of the electrophotographic photoreceptor using the plasma treatment has not been obtained. With respect to this, if the organic photoreceptor is directly exposed to plasma, properties of the photoreceptor may be reduced due to deterioration of a charge generation substance or a charge transport substance. Accordingly, there is the case where direct exposure of the organic photoreceptor to plasma is avoided.